Magnetostrictive transducer



May 16, 1961 N. MILLER MAGNETOSTRICTIVE TRANSDUCER 2 Sheets-Sheet 2 Filed July 14, 1944 INVENTOR LA YMON N. MILLER 2 ATTORNEY States 2,984,819 MAGNETOSTRICTIVE TRANSDUCER Filed July 14, 1944, Ser. No. 544,987

Claims. (Cl. 340-11) This invention relates to transducing devices, and particularly to an improved microphone especially adapted for receiving underwater sound of supersonic frequencies but capable of wider uses, including the generation and sending of such sound.

An important object of the invention is to provide such a transducing device which is rugged and reliable in character, which operates magnetostrictively, and which may be made to respond to a desired frequency band the width of which is selectable within wide limits.

A further object is the provision of such a microphone the directional characteristics of which are sharply defined but subject to variation, by simple engineering variations of the dimensions of structural components.

Other objects and advantages will be apparent upon consideration of the present disclosure in its entirety.

In the drawings:

Fig. l is a vertical sectional View of a microphone constructed in accordance with the principles of the present invention;

Fig. 2 is a schematic diagram of a suitable input circuit employed with the microphone of Fig. 1; r

Fig. 3 is a graph showing the frequency response of such a microphone;

Fig. 4 is a comparative graph showing curves indicative of the directional patterns of the microphone of Fig. 1 as compared with that of a crystal microphone, these being laid out against a curve representing the expected theoretical pattern;

Fig. 5 is a perspective view of the microphone;

Fig. 6 is an exploded perspective view of the internal components of the microphone, with the casing, cover and clamping ring removed;

Fig. 7 is a perspective view of one of the field magnet assemblies; and

Fig. 8 is a perspective view of the clamping ring.

The embodiment herein illustrated is adapted to be placed inside a cylindrical casing 15 through which the sound is required to pass to reach the microphone. A relatively heavy metallic ring 14 is fastened, as by soldering, to the inside of the casing. The bottom surface of the ring is shaped conformably to the curvature of the casing. A relatively heavy sound transmitting plate and diaphragm unit 1, the shape of the bottom of which also conforms to that of the casing, is held against the interior of the casing by a clamping ring 2 attached by screws 2' to the ring 14 and having a cylindrical flange 2" bearing downwardly against the perimeter of the relatively thin peripheral flange portion 1' which is integral with and projects from the heavier body portion 1. A sheet of resilient rubber 12 is interposed and somewhat compressed between the plate 1 and the casing, to distribute stresses and equalize the transmission of sound between all parts of the abutting surfaces of these elements. The rubber is preferably cemented to the diaphragm surface, although other methods of assuring uniform contact throughout may be used, including vulcanizing or the use atent ice of a castor oil film or the like, which film may be applied to both sides of the rubber.

Firmly attached to and projecting upwardly from the top surface of the plate 1 in accurately parallel relation are a plurality of resonant tubes 9, which may be of nickel or other suitable metal. -In the embodiment shown there are four in number and soldered in depressions 9' in the plate, in which depressions they fit accurately. The tubes are longitudinally slotted to prevent eddy current losses. In the embodiment shown the tubing is of outside diameter, .010" in thickness, the slot being approximately in width. The resonant frequency is determined by the length of the tube. In one embodiment of the invention the tubes are of equal lengths. They may be made with small variations of length in order to secure a variation in the frequency band. With the tube inserted /8 into the diaphragm plate, a total tube length of 2% will produce resonance at approximately 24.5 kilocycles, as indicated in Fig. 3. Where it is desired to provide a broader frequency range the tubes are made unequal in length.

Spacedly positioned above the diaphragm plate is a magnet and coil assembly, including a rod 13 of magnetic material such as Alnico projecting into each of the tubes 9 and an electromagnetic 'coil 8 surrounding each of the tubes. The tubes are spaced from the rods and from the forms 8 on which the coils are wound, the coils and forms being held and positioned by and between the insulating end plates 5, 6 and a cooperating top or clamp plate 7 which overlies the plate 6. Through these three plates extend elongated studs 11 threadedly attached or otherwise anchored at their lower ends to the flange 1' of the diaphragm plate. The bar magnets are held at their upper ends in flanged holders 10 proportioned to fit into the upper ends of the hollow cylindrical coil forms 8 and so maintain the magnets in centered positioning. The upper ends of the holders 10 project above plate 6 and are contacted by the lower surface of plate 7, which constitute mounting means for the magnet and coil assembly and when tightened down by means of nuts 11' applied to the upper ends of the studs 11, holds all of the components of said assembly rigidly in their indicated telescopic and coaxial relationship. Spacing sleeves 11 on the studs 11 maintain the coil and magnet assembly at a desired height above the diaphragm plate.

A casing is provided in the form of cylindrical sleeve and cover portions 3, 4, the former attached as by soldering at its lower end to the upper surface of the clamping ring 2 and the latter attached by screws to the sleeve.

The nickel tubes 9 may have their optimum magnetostrictive property developed by proper annealing or other heat treatment, and this condition must not be altered by the heat of soldering or by vulcanizing of the rubber 12. In assembly of the tubes to the diaphragm plate, therefore, soldering is preferably accomplished by heating the under side of the plate (before the rubber is attached). If the rubber is attached by vulcanizing, the heat must not be suflicient to :aifect the desired properties of the tubes.

Where the device is to be used under water, the Fe value of the rubber (density and rate of sound travel therein) should be substantially the same as that of water.

It is desirable to prevent sounds traveling laterally in the casing wall 15 from entering the diaphragm plate. This is eifectively done by the relatively thin section and angular disposition of the flanges 1', 2". Due to the relatively thin section of these parts, sound transmission is substantially restricted. One of the flanges lies transversely of the direction of vibration regardless of whether the sound waves are transverse or longitudinal with re- Pa'tented May 16, 1961 3 spect to the direction of their propagation through the casing.

In order to insure that the parts are not assembled in such manner that the resonant tubes touch either their coil assemblies or their magnets or magnet holders (which 'would decrease sensitivity and cause lack of uniformity of operation among the several tubes) means may be provided for checking each unit with an ohmmeter. This is efiected by painting an electrically conductive line of relatively high resistance as with Aquadag (graphite suspension in Water) along the inside length of the insulating coil form tubes 8, such lines being connected to rings of this material painted around the tops and bottoms of the insides of these tubes, all of these being connected by lines of the same material to the low side microphone contact. The resistance of such strips may be from 10,000 to 100,000 ohms, depending upon the length and thickness of the deposits. A continuity measure with the ohmmeter between the diaphragm or the casing 15 and the low side of the microphone cable 20 will thus tell if the tubes are touching. A complete open circuit indicates that all tubes are free of contact. A low resistance indicates contact. Since the magnet holders rest on the graphite layer, a short-circuit from the magnet to tube will also show up as a low resistance indication.

The coils 8 are connected in series, and are illustrated as a single coil in Fig. 2, which also shows fragmentarily the connected parts of a vacuum tube input circuit to which the microphone is connected and which may be arranged to excite or actuate desired apparatus. Since such circuit and apparatus form no part of my present invention, they will not be described in detail. A tuning condenser 21 may be included between the microphone and the control grid 23 of the vacuum tube 22. In Fig. 4 the uppermost curve is a representative pattern of a crystal microphone, the middle curve is the pattern of the instant magnetostrictive microphone while the lowermost curve is the theoretical pattern with which the first and second directional patterns are to be compared. The theoretical pattern is that of a 2.5" diameter piston at 24.0 kc. working in an infinite plane bafile consisting of a one-eighth inch steel sheet.

I claim:

1. In a transducer, a vibratory diaphragm, electromagnetic means confronting said diaphragm in axial perpendicularity, and a plurality of tubes of magnetostrictive material rigidly projecting from said diaphragm and coaxially occupying said electromagnetic means, said tubes being of variant resonant properties.

2. In a transducer, a vibratory diaphragm, electromagnetic means confronting said diaphragm in axial perpendicularity, and a plurality of tubes of magnetostrictive material rigidly projecting from said diaphragm and coaxially occupying said electromagnetic means, said tubes being of variant length to impart diverse fundamental frequencies thereto.

3. A transducer comprising a relatively heavy plate one face of which is confrontable with a portion of a con.-

' plate, supports erected from the second flange, and a permanent magnet and an electromagnet held in suspension by the supports, occupying proximate and spaced positions in respect to the tube, respectively on the inside and outside thereof.

4. In a transducer, a vibratory element, at least one magnetostrictive tube rigidly erected from said element, a permanent magnet centered within the tube, a flanged holder at one end of the magnet, an electromagnetic coil wound on a tubular form in which the holder is fitted to suspend the permanent magnet, and mounting means for the permanent magnet consisting of a pair of plates between which the flange of the holder is clamped, one end of the tubular form being set in one of said pair of plates.

5. In a transducer, a perimetrically flanged vibratory element, at least one magnetostrictive tube rigidly erected perpendicularly of said element, an electromagnet and a permanent magnet, a pair of plates between which the electromagnet is situated in spaced concentricity around the tube, a flanged holder at one end of the permanent magnet resting on one of the plates and spacedly centering said magnet in the tube, a clamp plate superimposed on the flange of the holder, and means mounted on the perimetric flange of the vibratory element including spacers rigidly holding the assembly of plates and magnets in their related positions.

References Cited in the file of this patent UNITED STATES PATENTS 942,897 Garrett et al Dec. 14, 1909 1,008,340 Howes Nov. 14, 1911 1,121,986 Davison Dec. 22, 1914 1,834,498 Parshall Dec. 1, 1931 1,882,398 Pierce Oct. 11, 1932 2,014,410 Pierce Sept. 17, 1935 2,063,944 Pierce Dec. 15, 1936 2,063,950 Steinberger Dec. 15, 1936 2,116,522 Kunze May 10, 1938 2,170,206 Mason Aug. 22, 1939 2,249,835 Lakatos July 22, 1941 2,328,496 Rocard Aug. 31, 1943 2,346,655 Beniotf Apr. 18, 1944 2,364,679 Williams Dec. 12, 1944 2,405,472 Tuttle Aug. 6, 1946 2,473,354 Beniofl June 14, 1949 FOREIGN PATENTS 498,637 Germany May 23, 1930 394,994 Great Britain July 5, 1933 

